Intent in Android Theory

An Android Intent can be used to perform following tasks :
Open another Activity or Service from the current Activity
Pass data between Activities and Services
Delegate responsibility to another application.

so if we wanna send an picture let say it shows by which app you wanna do like whatsapp, bluetooth, fb, share it etc. so it called explicit intent?? and how do we define our app to do so… like coe in that app list